The high-energy radiation generated by an x-ray source, a linear accelerator for instance, such as gamma, x-ray or photon radiation, is shielded by an adjustable diaphragm system, which generally consists of wolfram plates and the beam cross-section is formed, so-called “beam shaping” such that a target area, like a tumor for instance, is exposed to a maximum amount of radiation and surrounding healthy tissue is exposed to a minimum amount of radiation. To achieve the best possible adjustment of the beam cross-section to the target area, the multi-leaf collimator consists of a plurality, for instance several hundred, adjustable thin individual plates. The radiation path in a radiation therapy device consists of a high-energy radiation source, which generates and emits high-energy radiation, a linear accelerator for instance. One first simple electrically adjustable XY diaphragm system limits the radiation path such that the adjacent multi-leaf collimator in the radiation path is fully illuminated. The multi-leaf collimator then structures the beam cross-section such that a precisely predetermined region is radiated.
The optimization problem within radiation therapy consists in minimizing the radiation dose, to which the healthy tissue is exposed, and in at least maintaining it to below a harmful threshold and in simultaneously exposing cancerous tissue to a significantly harmful radiation dose. The methods for radiation treatment are thus very different and are undergoing constant development. Examples worth mentioning here are:                Conformal Radio Therapy (CRT),        Intensity-Modulated Radiation Therapy (IMRT),        Image-Guided Radiation Therapy (IGRT) Gated treatments,        High-precision radiation therapy and radiation surgery (SRT/SRS),        Future advanced adaptive therapies, such as Dose-Guided Radiation Therapy (DGRT), as they become available.        
The objectives here are to increase selectivity, expand the application bandwidths, such as radiating moving target areas for instance, increasing the operating reliability, such as increasing/extending the service intervals and shortening the treatment duration, such as for instance by “sliding window”. In particular, the latter method not only reduces the radiation exposure of the healthy tissue, but also influences the workflow and efficiency of the large devices. The following profile of requirements results herefrom for multi-leaf collimators:                High positioning accuracy of the wolfram plates (previously type 0.1 mm),        High movement speed of the wolfram plates (previously type 18 mm/s),        High acceleration of the wolfram plates (previously type 38 mm/s2),        High operating reliability/maintenance intervals (life-cycle costs).        
DC motors with front-sided planetary gears are currently used as multi-leaf drives with a reduction of 1:275 for instance and a torque of 0.84 Nm at a maximum of 0.44 rps, said DC motors being arranged in groups of type 40 motors and driving the wolfram diaphragms over slanted-toothed helical pinions. Two linear potentiometers are present per diaphragm in order to control and monitor the position. The positioning accuracy amounts to 0.5 mm in the isocenter, which corresponds to a control accuracy of the plates of 0.25 mm.
The prior art consists in radiating cancerous tissue from different spatial directions, with the so-called “step and shoot” strategy being used. The system is thus paused for each new adjustment. In this way, a spatial direction is displaced, the multi-leaf collimator is set up to generate the optimum beam cross-section, and radiates according to a previously determined radiation dose, the next position is displaced and the multi-leaf collimator is set up again etc. A very long treatment duration results due to the added setup times for the individual illuminations.
The aim is to radiate continuously using a rotating gantry/frame and a dynamically variable multi-leaf collimator with a “sliding-window”. For devices of the next generation, higher adjustment speeds of more than 20 mm/s are aimed at while simultaneously improving plate positioning accuracy by more than 0.10 mm. These requirements are not restricted or only to a minimum degree using current drive technology and can be costly to display.
The problem involved with using electrical motors for displacing the metal plates consists in the high moment of inertia of the rotor, the high rotor speed and thus a high rotation energy, thereby resulting in poor dynamic characteristics. For this reason, braking or reversing the direction of movement of the metal plates is associated with relatively large delay times. In order to reduce the high rotor speed from type 10,000 rpm to a typical output speed of 60 rpm, electric motors also require a multi-stage gear. As a result of the unavoidable gearbox clearance, the positioning accuracy of the output is restricted, also in fact when an additional sensor is used for position detection purposes.